8. Hard Time - Star Trek Deep Space Nine
Hard Time is a fourth season episode of Star Trek Deep Space Nine. While it is about as grim as it gets for Chief O'Brien (definitely falling into the 'O'Brien Must Suffer' camp), there is a bittersweet thread that runs through the episode that makes the entire endeavor worthwhile.
O'Brien is charged with espionage and is sentenced to twenty years' worth of memories of imprisonment to be beamed into his mind. The process is irreversible (think a mirror version of The Inner Light). When we meet him in the beginning of the episode, the procedure is complete and the next forty minutes are spent telling the story of his time inside, illuminating his outbursts and struggles as he goes.
He has lost all control of his temper from the trials that he faced with Ichar, the cellmate who was also beamed into his mind. The final scene between O'Brien, Bashir and Ichar in the cargo bay is both heartbreaking and another great example of the friendship that O'Brien and Bashir share.